(1) Field of the Invention
The present invention relates to a liquid crystal display device, and in particular, to a liquid crystal display device where a common symmetric method, such as a dot inverting method, is adopted as the method for driving the liquid crystal display device.
(2) Description of the Related Art
TFT type liquid crystal display devices where thin film transistors are used as active elements can display images with high definition, and therefore are often used as the display devices for televisions and personal computers.
Liquid crystal display devices basically have a so-called liquid crystal display panel where a liquid crystal layer is sandwiched between two (a pair of) substrates, at least one of which is made of transparent glass or the like, and a predetermined pixel is turned on and off by selectively applying a voltage to various types of electrodes that form pixels on the substrates of this liquid crystal display panel, and thus, the liquid crystal display devices are excellent in contrast performance and high speed display performance.
When the same voltage (direct current voltage) is applied to a liquid crystal layer for a long period of time, the inclination of the liquid crystal layer is fixed, which consequentially causes an afterimage and shortens the life of the liquid crystal layer. In order to prevent this, liquid crystal display devices use an alternating current having a certain period of time for the voltage applied to the liquid crystal layer, that is to say, the voltage applied to pixel electrodes is switched from the positive voltage to the negative voltage or vice versa during a certain period of time with the common voltage (VCOM) supplied to the counter electrodes as a reference.
Two methods, a common symmetric method and a common inverting method, are known as methods for driving the liquid crystal display device according to which an alternating current voltage is applied to the liquid crystal layer (see below Japanese Unexamined Patent Publication 2009-15334).
The common symmetric method is a method for keeping the common voltage (VCOM) supplied to the counter electrodes constant and for inverting the voltage applied to pixel electrodes (that is to say, gradation voltage) to a voltage at a potential higher than the common voltage (VCOM) or to a voltage at a potential lower than the common voltage (VCOM), and a dot inverting method and an n line (two line, for example) inverting method are known as examples of this method.
(Patent Document 1) Japanese Unexamined Patent Publication 2009-15334